This invention relates to a rotary multi-phase electrical machine, such as a three-phase AC generator and a three-phase AC motor and more particularly to an improved coil winding arrangement therefore.
Three-phase AC generators or motors are well known for many applications. Brushless electric motors are examples of machines of this type. In the conventional rotary electric machine, connected coil winding coils formed on magnetic pole teeth cooperate with permanent magnets. Upon relative rotation of the coil windings and permanent magnets, an electromotive force is induced in each coil (in the case of a generator) or a torque is generated in the rotor (in the case of a motor). The electromotive force or a counter electromotive force generated in each phase or line is the vector sum of effects of the coils in each phase or line.
In rotary electric machines widely used in home appliances or for industrial applications, the supply or output voltage is relatively high. Thus, it is possible to use for the coil windings a flexible winding having a small diameter wound on the magnetic pole teeth in each phase or line. These windings are connected normally in series with either a Y-connection or a Δ-connection. The winding directions of the stator coils are alternated so that the polarities of the coils may be the same.
In addition to home or industrial application, these types of rotary electric machines are widely used in vehicles such as automobiles and motorcycles. For example, blushless motors are employed as a power source for an electric vehicle or the like. In general, the supply voltage in such a vehicle is lower than those for home or industrial uses. Thus, a heavy current must be applied to obtain a high power. Therefore, in a rotary electric machine for a vehicle, the number of turns of a coil wire wound on each core is relatively small, and the diameter of the coil wire is relatively large.
However, when a coil wire having a large diameter is used, the efficiency of winding the coil wire on magnetic pole teeth is significantly lowered. Also, the ends of coil wires in each phase must be connected at coil ends and a neutral connection must be made. The resulting processing is slow and difficult resulting in reduced production capacity and high cost. Additionally, the connections at coil terminals are unavoidably large, resulting in a large-size winding assembly and consequently, a large generator or motor.
It is possible to connect the coils in each phase in parallel to lower the current therein. If this is done, a winding having a smaller diameter can be employed. This permits the number of turns of each coil to be increased. Because the voltage is low in rotary electric machine used in vehicles, the increase in number of turns can be relatively small.
However, it has been found that, when the coils of each phase are connected in parallel, a circulating current is generated in a closed circuit formed of the coils connected in parallel by a phase difference of an electromotive force or a counter electromotive force generated in each coil, resulting in performance deterioration.
It is, therefore, a principal object of this invention to provide a permanent magnet type three-phase AC rotary electric machine that has parallel windings, but also prevents or reduces any circulating current from flowing.
It is a further object of this invention to provide a permanent magnet type three-phase AC rotary electric machine having a small diameter coil windings to permit reduction in the size of the machine.